The present disclosure relates to a solid-state imaging device, an imaging apparatus, and an electronic apparatus, and particularly, to a solid-state imaging device, an imaging apparatus, and an electronic apparatus, capable of allowing an influence by nonlinearity latent in output of an amplification transistor output by a current transmission system to be improved with a simpler circuit structure in output of pixel signals from a floating diffusion.
In a column system adopted as a typical CMOS (Complementary Metal-Oxide Semiconductor) image sensor, light incident on each unit pixel is output from a signal line as a pixel signal per pixel in such a manner that the light is photoelectrically converted by a photodiode to generate a signal charge, the signal charge is transferred to a floating diffusion by a transfer transistor, and a potential variation of the floating diffusion is converted into a signal voltage and simultaneously amplified by an amplification transistor.
Here, the floating diffusion is connected to a gate of the amplification transistor. A source of the amplification transistor is connected to a load transistor (current source) and a drain of the amplification transistor is connected to a power source.
In this case, the amplification transistor and the load transistor constitute a source follower circuit. That is, a voltage variation in the gate of the amplification transistor is drawn to the source of the amplification transistor as a voltage amplitude at about one times, and a voltage signal is output to a next stage as a pixel signal.
This is generally referred to as a voltage transmission system. In the voltage transmission system, it is necessary to increase mutual conductance of the amplification transistor in order to realize high bandwidth, but the mutual conductance may not be freely adjusted since a ratio (W/L) of a channel width W to a channel length L in the amplification transistor is determined from conversion efficiency at the floating diffusion.
In addition, when only a source current of the amplification transistor is increased, a gate-source voltage of the amplification transistor becomes larger and a voltage drop also becomes larger. For this reason, a subsequent DC (Direct Current) circuit design (direct current circuit design) is difficult considering an output dynamic range.
That is, since the source current of the amplification transistor may not be excessively increased, it is difficult to realize high bandwidth.
As countermeasures, a current transmission system is proposed in which a voltage is fixed as in a diode or the like so that a current is drawn, without current source connection of a source of an amplification transistor.
Since this circuit may simply increase the current by adjusting a channel width W of the diode, high bandwidth is easily realized. In addition, since a voltage variation is very small relative to an input dynamic range, a subsequent DC circuit design is also easily performed (see ITE Technical Report Vol. 24, No. 27, PP. 1-4, March, 2000).
The drawn current is converted into a voltage signal by an IV amplification conversion circuit (current-voltage amplification conversion circuit) and is used. This is the current transmission system.
However, the source current of the amplification transistor has nonlinear characteristics with respect to a voltage variation of a floating diffusion.
In this case, gain deterioration occurs when output impedance of the IV amplification conversion circuit is not lowered. Accordingly, an impedance conversion circuit is necessary as a countermeasure (see Japanese Unexamined Patent Application Publication No. 2004-023135).